Talk:Multimode distortion

From Wikipedia, the free encyclopedia

[edit] Terminology

I can see that 1037C definitely states that the term "multimode distortion" is correct, and "multimode dispersion" wrong, but I don't think that's reality. I mean, I think that 1037C is trying to make a prescriptive definition, not to describe the language that actual engineers and physicists use. For example, "multimode distortion": 898 Google hits. "modal distortion" 374 Ghits. "multimode dispersion": 686 Ghits. "modal dispersion": 47,700 Ghits.

On IEEE Xplore (journal and proceedings search) "multimode distortion": no results. "modal distortion": 6 results. "intermodal distortion": 2 results. "modal dispersion": 93 results. "multimode dispersion": 4 results. "intermodal dispersion": 33 results. These results seem really low -- I'll try again tomorrow from work where I can use the advanced search.

I've also seen before that 1037C has a different definition of terms than any engineers or academics I've worked with. On "Transmission lines" vs "waveguides" it defines transmission lines as anything that carries power or signal, and therefore makes waveguides a subset of transmission lines. I don't know anyone who actually uses the terms that way.

Bottom line, 1037C definitions might be correct if you're writing a tender for a US Government contract, but they're not trustworthy for usage in practice, and they shouldn't be considered as uncontestably authoritative in Wikipedia. -- The Photon 05:28, 31 October 2006 (UTC)

Good points. Actually, I discovered after I imported this that there is a section on modal dispersion at dispersion (optics). I'm still evaluating what to do.--Srleffler 06:11, 31 October 2006 (UTC)

[edit] Merging

OK, I think I'm going to try to merge the threads of an article here for now. If desired, we can move it to modal dispersion or whatever other title is desired. The following section is clipped out of dispersion (optics) for merging here. It was misplaced at the top of the dispersion article anyway. The topic is certainly distinct enough to have its own article, and not be comingled with regular dispersion.

Modal dispersion in optics

Different optical systems have different numbers of modes. In the optical fiber case, the number of supported modes depends on the Numerical aperture. With a larger Numerical aperture, the cone of accepted angle is larger, allowing for light to enter the fiber from more angles. These different angles of incidence to the fiber's core allow some wavelengths to travel rather directly through the fiber and other wavelengths to reflect off of the cladding more frequently. This variance in path-length causes modal dispersion.

This dispersion of path length between modes can cause an inputted pulse of information to become spread-out as different components of the pulse will vary from the average pulse speed. Pulse-spreading introduced by multiple modes causes interference between adjacent bits of information, presenting a limit to the information capacity of a transmitted signal.